1. Field of the Invention
The present invention relates to an adhesive resin composition for producing a laminate having improved properties including gas barrier properties (oxygen, carbon dioxide, etc.), resistance to contents (flavor and perfume retaining properties), good external appearance (surface gloss and transparency), mechanical strength, extendability, shrinkability, heat sealability, and interlayer adhesive strength, the laminate, a production method thereof and an oriented film obtained by orienting the laminate.
2. Description of the Related Art
Polyolefin (PO) type resins such as polypropylene, polyethylene, and ethylene-vinyl acetate copolymer have been widely used in a variety of fields. These PO type resins show good moldability, mechanical strength, chemical resistance and heat sealability. However, they show poor gas barrier properties and flavor maintaining properties, and sometimes they show inferior external appearance (surface gloss and transparency) depending on the molding methods and the kinds of the resins.
As a means to ameliorate such defects, lamination of PO type resins with polyamide (PA) type resins or ethylene-vinyl acetate copolymer saponified products (EVOH) which have excellent gas-barrier properties, or lamination with polyester (PES) type resins, for improving the resistance to contents or external appearance, have been proposed.
As PO type resins are nonpolar, the interlayer adhesive strengths of the laminates obtained by directly laminating them with EVOH, PA type resins and PES type resins are so low that the laminates cannot be employed in practical uses.
Accordingly, lamination methods utilizing various adhesives have been proposed.
For example, polyolefin type adhesive resins modified with unsaturated carboxylic acids and the like have been proposed for adhesion of PO type resins with polar resins such as EVOH and PA type resins.
For producing laminates of PO type resins with resins other than EVOH and
type resins, i.e., the laminates of PO type resins with PES type resins, polycarbonate (PC) type resins, and acrylic resins or polystyrene (PS) type resins, and laminates of PS type resins with EVOH, PA type resins, and PES type resins, such lamination methods have been proposed as: a method in which a composition comprising an olefin type polymer and an alicyclic or aromatic polymer (as a tackifier) is used as an adhesive (Japanese Patent Laid-Open No. 50-116536), a lamination method in which a composition comprising ethylene-vinyl acetate copolymer (EVA) and a tackifier is used as an adhesive (Japanese Patent Laid-Open No. 53-147733, Japanese Patent Laid-Open No. 54-10384 and the like); a lamination method in which a composition comprising EVA, modified polyolefin and an aliphatic petroleum resin (as a tackifier) is used as an adhesive (Japanese Patent Laid-Open No. 53-127546); a lamination method in which a composition comprising a modified ethylene-.alpha.-olefin random copolymer of low crystallinity and a tackifier is used as an adhesive (Japanese Patent Laid-Open No. 61-241144); a lamination method in which a composition comprising a low density ethylene-.alpha.-olefin random copolymer of low crystallinity, a tackifier and a modified polyethylene is used as an adhesive (Japanese Patent Laid-Open No. 61-162539); a lamination method in which a hot-melt adhesive composition comprising a mixture of a styrene type thermoplastic elastomer, a tackifier, a low molecular weight polypropylene and a process oil is used as an adhesive (Japanese Patent Laid-Open No. 1-144483); and a lamination method in which a hot-mel type adhesive composition comprising a styrene type thermoplastic elastomer, an alicyclic adhesive, and a cyclic olefin random copolymer is used as an adhesive (Japanese Patent Laid-Open No. 3-223381).
Also recently, in order to further improve the performances of various wrapping materials, orientation of a coextruded product has been proposed to improve the strength and the gas barrier properties thereof or for applications in the field of shrink packaging. Also, the use of maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, maleic anhydride modified ethylene-vinyl acetate copolymer, maleic anhydride modified ethylene-1-butene copolymer, styrene modified amorphous ethylene-propylene copolymer, and a hydrogenated product of maleic anhydride modified styrene-butadiene copolymer in an oriented laminate film has been proposed. A production method thereof (Japanese Patent Laid-Open No. 52-146487), a heat shrinkable multilayer film and a packaged body thereof (Japanese Patent Laid-Open Nos. 57-205147 and 58-8644), a heat shrinkable multilayer film and a production method thereof (Japanese Patent Laid-Open No. 59-152853), a biaxially oriented molded body of a thermoplastic polyester composition (Japanese Patent Laid-Open No. 60-76325), a production method of a biaxially oriented laminate (Japanese Patent Laid-Open No. 60-82324), a heat shrink packaging film (Japanese Patent Laid-Open No. 61-94753) and the like have also been proposed.
However, when cooled and hardened then heated again and oriented in both machine direction and cross direction at least 1.5 times or more, a coextruded body produced by any method shows an extremely lowered adhesive strength, far from the practically usable level. Additionally, though the adhesive strength may reach the practically usable level at a normal temperature, the laminate has poor moldability and in the case of hot-fill etc. shows a low adhesive strength at an elevated temperature, so they have many problems in their use at the moment.
On the other hand, PES films, silica deposited films, biaxially oriented polypropylene films, PA films, EVOH films or sheets or metal foils such as aluminium foil or copper foil have excellent resistance to gas transmission as well as excellent rigidity, thus they have been widely used mainly for packaging foods. Further, they can be laminated on metal such as copper, steel to avoid rusting. However, for practical use, it has been proposed to laminate even such unoriented, uniaxially or biaxially oriented films with PO films or polyethylene terephthalate films to prevent deterioration at a high temperature or for imparting heat sealablity, with EVOH or PA to improve resistance to gas transmission and with PC or PS and the like to improve rigidity.
Conventionally, for laminating the above-mentioned resin film, sheet or metal with the above-mentioned resin layer, either an anchor coat agent must be coated on such a resin film, sheet or metal in advance and the resin layer laminated thereon by an extrusion laminating method; or the resin film, sheet or the metal and the resin layer must be bonded together using a dry laminate adhesive. With such methods, an anchor coat agent or an adhesive is necessary in either case, thus it has been difficult to simplify the lamination process.
Further, a method has been proposed in which a resin film, sheet or a metal and a resin layer are subjected to coextrusion lamination using a low-density polyethylene as an adhesive resin layer, however, with such a process, it has not been possible to obtain sufficient interlayer adhesive strength.
Also, using a polyolefin resin, wherein polar groups are introduced, as an adhesive resin layer (see for example, Japanese Patent Publication No. 60-28658) has been studied, but use of the polyolefin resin, wherein polar groups are introduced, as the adhesive resin layer cannot eliminate the problem since preheating or after heating of the adherend for the coextrusion lamination is still required.
In consideration of the above-mentioned situation, an object of the present invention is to provide an adhesive resin composition having excellent adhesive strength with EVOH, PA type resins, PO type resins, PS type resins, PES type resins, acrylic resins, and PC type resins (even following orientation treatment), and excellent extrudability in the form of a film, sheet, extrusion-blowing and the like, a laminate obtained therefrom, and an oriented film of the laminate.
Another object of the present invention is to provide a laminate having enough interlayer adhesive strength which is obtained by coextrusion lamination of a resin film, sheet or a metal and a resin layer without carrying out preheating or after-heating of the adherend, and a production method thereof.